In 1993, the first news of a nearly complete, one-meter-long skeleton of an
early bipedal dinosaur was published (Sereno et al. 1993). This was
Eoraptor lunensis, a medium-sized carnivore found in the
Ischigualasto
Formation of northwestern Argentina. The find occurs
alongside other early dinosaurs and their kin, such as
Herrerasaurus and Pisanosaurus.

Eoraptor lacks the specialized features of any of the major groups of
dinosaurs, and is quite
similar to what would be expected for dinosaur ancestors. This has
led some to conclude that it is not part of the dinosaurs proper,
but is a closely related archosaur.
Others have pointed to the functionally three-fingered hand as an indication
of close ties to theropod dinosaurs.

In any case, the traits of Eoraptor suggest that the first dinosaurs
were small, bipedal predators. Taken together, the finds at
Ischigualasto demonstrate that dinosaurs had radiated by the Late
Triassic.